168 STUDY OF COMMON PLANTS. 



form and structure. Is any mechanical principle involved 

 in the disposition of material ? Observe the number and 

 position of the nodes (parts of the stem to which the leaves 

 are attached). Do they contribute in any way to the 

 strength of the structure ? 



Bend the culm through several degrees, after stripping 

 off the leaves. Where are the weakest parts ? Is there 

 any special protection or support for these parts ? 



Taken as a whole, is the stem satisfactorily constructed to 

 sustain the weight of the head and resist the stress of winds? 



Note. — Microscopic examination sliows a simple but effective arrange- 

 ment of the mechanical elements of the culm, by which great strength is 

 secured with a minimum of material.' 



III. Take up next the relation of leaves and stem. 

 How are the leaves attached ? Are their sheaths entire or 

 slit ? What is the leaf arrangement ? 



IV. Note the form and structure of the leaves, and the 

 manner in which they twist in drying.^ 



Notice the appendage of the leaf at the angle made by 

 the blade and culm. What is it morphologically, and 

 what is it called ? ^ 



Inflorescence and Flowers. 



I. Notice first the general features of the inflorescence. 

 It has the form of a thickened spike, composed of many 

 spikelets. The latter are arranged alternately on each side of 

 a " zigzag, jointed, channelled rachis." Remove half a dozen 

 or more of the lower spikelets to make this more obvious. 



II. Study next the structure of one of the spikelets. 

 Each spikelet includes several flowers and is subtended by 



1 Cf. Haberlandt, Physiologische Pftanzenanatomie, p. 114 et seq. 

 '' Cf. Beal, Grasses of North America, p. 29 et seq. 

 3 Cf. Gray, Structural 'Botany, p. 106. 



